1. Field of the Invention
This invention relates to X-ray detectors. More particularly, it relates to a method of fabricating an X-ray detecting device with reduced breakage of a transparent electrode.
2. Discussion of the Related Art
X-ray imaging systems typically produce photographs of objects using X-rays. Such systems have been successfully used for medical, scientific, and industrial applications. While photographic films are usually used, another type of X-ray imaging system uses X-ray detecting panels that convert X-rays into electrical signals. Such an X-ray detecting panel is illustrated in FIG. 1. As shown, that panel includes a photosensitive layer 6 for converting X-rays into electrical signals, and a thin film transistor substrate 4 that selectively outputs those electrical signals.
The thin film transistor substrate 4 includes pixel electrodes 5, which are arranged in pixel units, and thin film transistors (TFT's), each of which is connected to a charging capacitor Cst, to a gate line 3, and to a data line (which is not shown). On the upper portion of the photo sensitive layer 6 is a dielectric layer 7 and an upper electrode 8. The upper electrode 8 is connected to a high voltage generator 9.
The photosensitive layer 6 is usually comprised of selenium that is hundreds of microns thickness. That photosensitive layer detects incident X-rays and converts them into electrical signals. When doing this, the photosensitive layer 6 produces electron-hole pairs in response to the incident X-rays. The electron-hole pairs are separated by a high voltage (several kV) that is applied to the upper electrode 8 by the high voltage generator 9. Holes are stored in the charging capacitors Cst by way of the pixel electrodes 5. However, some holes accumulate on the surfaces of the pixel electrodes 5. This results in fewer holes being stored in the charging capacitor Cst. To prevent this, a charge-blocking layer 11 is formed on each pixel electrode 5. The thin film transistors (TFT) respond to gate signals input on the gate line 3 by applying pixel signals from the charging capacitor Cst to the data line. Those pixel signals are applied, via a data reproducer, to a display device that produces an image.
FIG. 2 is a plan view showing a structure of a conventional X-ray detecting device in a way that emphasizes a thin film transistor part and a storage capacitor part. As shown, a substrate 2 is provided with a gate electrode 12, a gate insulating film 32 over the substrate and over the gate electrode, and a semiconductor layer 34. Over the semiconductor layer 34 is a source electrode 14 and a drain electrode 16. In order to protect the thin film transistor, a storage insulating film 38, and first and second protective films 40 and 36 are formed over the thin film transistor. A first drain contact hole 15a passes through the storage insulating film 38, while a second drain contact hole 15b passes through the first and second protective films 40 and 36. The drain electrode 16 electrically contacts a drain transparent electrode 27 via the first drain contact hole 15a. Further, the drain transparent electrode 27 electrically contacts the pixel electrode 5 via the second contact hole 15b. Thus, the drain electrode 16 is in electrical contact with the pixel electrode 5 via the first and second contact holes 15a and 15b. 
The charge capacitor part Cst consists of a storage electrode 25, the pixel electrode 5, which is positioned over the storage electrode 25, and the interposed second protective film 36. Below the storage electrode 25 is a ground line 22 for resetting residual charges on the charging capacitor Cst. The ground line 22 and the storage electrode 25 are in electrical contact via a storage contact hole 17 that passes through the storage insulating film 38 and the first protective film 40.
FIG. 3A to FIG. 3G are section views showing a method of fabricating the X-ray detecting device of FIG. 2. First, the gate electrode 12 is formed by sequentially depositing first and second gate metals 12a and 12b onto the substrate 2, and then patterning those metals as shown in FIG. 3A.
Referring now to FIG. 3B, the gate insulating film 32, an active layer 34a, and an ohmic contact layer 34b are then formed by depositing an insulating material, and first and second semiconductor materials over the substrate 2 (including over the gate electrode 12), and then patterning the first and second semiconductor materials to form a semiconductor layer 34.
After formation of the semiconductor layer 34, as shown in FIG. 3C, the source 14, the drain electrode 16, and the ground line 22 are formed by first depositing a data metal onto the gate insulating film 32 and then patterning the data metal.
Referring now to FIG. 3D, the storage insulating film 38 and the first protective film 40 are then formed by depositing first and second insulating materials over the substrate 2, including over the source electrode 14, the drain electrode 16 and the ground line 22. The first drain contact hole 15a and the storage contact hole 17 are then defined by patterning the storage insulating film 38 and the first protective film 40. FIG. 3D will be referred back again.
Then, as shown in FIG. 3E, a transparent drain electrode 27 and a storage electrode 25 that are, respectively, in contact with the drain electrode 16 and the ground line 22, are then formed by depositing a data metal on the first protective film 40 and then by patterning that data metal.
As shown in FIG. 3F, the second protective film 36 and the second drain contact hole 15b are then formed by depositing an insulating material on the first protective film 40, and then by patterning that insulating material to form the drain contact hole 15b. 
Finally, as shown in FIG. 3G, the pixel electrode 5, which is electrically connected to the transparent drain electrode 27 via the second drain contact hole 15b, is formed by depositing a transparent conductive material onto the second protective film 36, and then by patterning that transparent conductive material.
Referring once again to FIG. 3D, the first drain contact hole 15a and the storage contact hole 17 are typically formed by simultaneously patterning the storage insulating film 38 and the first protective film 40 using dry etching. The storage insulating film 38 and the first protective film 40 are formed from an inorganic insulating material and from an organic material that generally have different etching rates. The etching rate of the storage insulating film 38 is usually faster than that of the first protective film 40, resulting in over-etching of the storage insulating film 38 in comparison with the first protective film 40. This causes an undercut phenomenon, shown in the expanded view of FIG. 3D, that results in the transparent conductive material deposited on the first protective film 40 (reference FIG. 3F) having poor coverage, thereby creating breakage problems at the transparent drain electrode 27 and the storage electrode 25.